A Goldilocks climate at home could protect you from COVID this winter
When lockdown rules were in full force early in the pandemic, little thought was given to how the humidity of the spaces we were locked in affected transmission of COVID-19.
But new research from MIT now suggests that relative humidity — or the percentage of moisture in the air compared to the maximum water the air can hold at a given temperature — could be a key metric in influencing transmission of the virus .
Maintaining indoor relative humidity between 40% and 60% — a Goldilocks climate, not too humid, not too dry — is associated with relatively lower rates of COVID-19 infection and death, according to a study published by MIT researchers Journal of the Royal Society Interface found. Researchers also discovered that relative humidity outside of these conditions was associated with poorer COVID-19 outcomes.
This “sweet spot” of humidity, as researchers call it, is outside the barometer of what most people find comfortable, which is around 30% to 50% relative humidity. To put it in context, an airplane cabin is kept at around 20% relative humidity.
The study adds another dimension to why cases of the COVID-19 virus soar during the colder months of the year. As COVID cases ebb and flow throughout the year, studies attempting to pinpoint the exact pattern of the virus in relation to outdoor seasonal conditions have “returned mixed results,” MIT scientists say.
How they measured the study
The MIT study measured COVID cases from 121 countries between January 2020 and August 2020 at the beginning of the pandemic, when vaccines were not yet available.
At the time, researchers noted that most societies spent more than 90% of their time indoors, where the vast majority of virus transmission occurred and climate control systems likely altered indoor humidity levels.
The researchers measured the number of COVID cases and deaths in countries that had an outbreak during this period, taking into account variables such as isolation, quarantine and testing measures. They then measured meteorological data and indoor relative humidity by comparing the outside temperature to the likelihood that people would turn on air conditioning when temperatures fell outside of the typical human comfort range of 66°F to 77°F.
They found that whenever a region had seen a significant increase in COVID-19 cases and deaths, the estimated indoor relative humidity in that region had exceeded the 40% and 60% limits. Almost all regions in the study had fewer COVID cases and deaths when they were in the humidity “sweet spot” during warmer periods, suggesting a strong correlation between regional outbreaks and indoor relative humidity.
“This mean indoor relative humidity may have a protective effect,” says the study’s lead author Connor Verheyen, a Ph.D. Medical Engineering and Medical Physics student in the Harvard MIT program.
In more regionally focused data, Verheyen and other researchers found that when indoor relative humidity fell below 40% in countries in the northern and southern hemispheres during their colder months, COVID-19 cases and deaths in those regions also rose. For countries in the tropics, where relative humidity would increase during the region’s summer season, there was also a gradual increase in COVID-19 deaths during this period.
“Indoor ventilation is still critical,” says Lydia Bourouiba, co-author of another study, who is director of the Fluid Dynamics of Disease Transmission Laboratory at MIT. However, she notes, “We find that maintaining an indoor relative humidity level at that sweet spot — from 40 to 60 percent — is associated with a reduction in COVID-19 cases and deaths.”
The researchers say their next step is to measure how indoor relative humidity affects outcomes from COVID-19 and find out whether pathogens in respiratory droplets survive longer in very dry or very humid conditions.
White House Medical Advisor Anthony Fauci made the announcement last week Conversations about healthcare Radio show that the US is at a difficult crossroads from COVID as the cold winter months approach and immune-avoidable variants of Omicron emerge.
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